Earlier forms of this character is just a combination of those characters.

What we see is the sun over the character for correct. There is a debate about the history behind this. To me the most plausible suggestion is that the ideograph locates the sun 日 over the character for right and correct, 正 ( this modified to the alternative form). The sun is the standard for correctness since it always on time will show up at the horizon. The sun also corrects tells us the time and the season of the year. Chinese people where very good in studying the planets and especially the sun since the agriculture where dependant on knowing when to plant and when to harvest.

Other more philosophical persons suggest that the sun is the exact reason we can exist on this planet and hence the meaning of am, are, is, right. I can see the sun, therefore I am so to say.